Movements of Adult Polydora websteri in Sediment along a Temperature Gradient Kaitlyn Dunham, Old Town High School otherwise.) Then there are two isolated 15.2 by 31.1 tanks on each side with an 45.7 by 27.9 tank in the middle. I created this system by siliconing two pieces of 29.2 by 27.9 glass into the original tank, creating two equal smaller reservoirs on both sides of the temperature gradient section of the tank (Figure 1). Water in the left reservoir was chilled while water in the right reservoir was heated. The reservoirs were chilled and heated by Yescom Aquarium 75W Fish Tank Thermostatic Chiller/Heaters with 3-Watt pumps. Blue food coloring was put in the cold reservoir and red food coloring in the hot reservoir. This was done so if there was a leak into the middle tank it could easily be identified where the leak was coming from. Also, in both side reservoirs a HOBO temperature logger took the temperature every three hours to show how consistent the reservoir temperatures were. A mixture of crushed oyster shells and freeze-thawed sediment was put into the bottom of the middle tank. The freeze-thawed sediment went through four 24-hour periods in and out of the freezer. Then the bottom of the middle tank was split into fifteen 8.9 by 8.9 quadrants. Styrofoam pieces were cut to help insulate the tank and to create a larger temperature gradient. Two 19.1 by 29.2 pieces were cut for the front part of the tank so that they covered the two isolated reservoirs on the side, then two 31.1 by 29.2 pieces were cut to cover the sides of the tank; lastly one 81.3 by 29.2 piece was cut to cover the entire
Introduction Polydora websteri is a species of Polychaete worm in the Spionidae family. The worms infest oysters by settling on shells as the larvae metamorphose to adults. This is a problem for oyster farmers all over the world. In this project I aimed to figure out if P. websteri adults prefer a certain sediment temperature and if they will move in the sediment to that preferred temperature. This research is important because not enough is known about P. websteri ecology in estuaries. Scientists and growers wonder if adults can complete their life cycle either in shells or in the sediment, releasing larvae into the water column from the sediment like the sediment-dwelling Polydora cornuta, which is very similar to P. websteri. Although little is known about P. websteri as sediment dwellers, Stanley Rice and others have observed that the adults can live in sediment in a petri dish, outside of a mollusk shell, but these observations were for short periods of time. If there is a preferred sediment temperature, that information could be useful to marine biologists and oyster growers. Another question scientists are asking is if P. websteri populations everywhere are all one species or if there are different species within the P. websteri category. If some P. websteri could live their entire life in the sediment then this knowledge may help scientists design experiments to look into the species question. Additionally, there could be important information in the sediment where P. websteri choose to live that could answer other questions about this worm. This knowledge could also lead to aquaculture practices that might help oyster farmers reduce the number of worms in their oysters. Investigating behaviors of adult P. websteri as sediment dwellers could be an important first step. I engineered an apparatus that would present adult P. websteri with a temperature gradient in sediment and track their movements along the temperature gradient.
Methods The experimental set-up involves one 76.2 by 31.8 glass tank with a depth of 33 centimeters. (All measurements are in centimeters unless noted
Figure 1: The tank as it was being built. The books are there simply to hold the glass together until the silicone dried. The two small tanks on the sides are the hot and cold reservoirs and the big tank in the middle became the temperature gradient section. 1
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Introduction to Scientific Research 2015–2016, Old Town High School
Figure 2: The insulation as it was being installed. The insulation scheme was designed to maintain steady cold and hot temperatures in the side reservoirs, and a stable temperature gradient across the middle tank. The grid written on the front piece of glass shows the layout of the five temperature zones that were used to measure the temperature gradient. Temperatures were monitored in three quadrants within each zone. back of the tank. They were then siliconed to the outside of the tank and were left to dry for 24 hours (Figure 2). After the salinity got to a safe level of around 30 parts per thousand, P. websteri were put into the experiment. The worms were retrieved by putting oyster shells into a magnesium chloride mixture which “drugged” the worms which made them come out of their burrows. Once the worms came out of the burrow they would be sucked up into a small pipette and then placed into the middle of a quadrant (Figure 3). Every other day the worms were fed 10 mL of a live culture of Tetraselmis and Isochrysis algae that we grew in the lab. Then the worms’ movements were monitored for the next 72 hours and documented by taking pictures of the worm tracks in the sediment. The data were collected for approximately three weeks. The pictures were put into a Google slide and the direction and distance the worms moved were documented. Also, every other day temperatures were taken of all the 15 quadrants and then graphed as box plots to measure the variability of the temperatures within a zone and to show the overall the overall temperature gradient.
Figure 3: The red ring in this figure shows a Polydora websteri coming out of its burrow in an oyster shell. The worm and oyster are in a magnesium chloride solution that has been used to drug the worm and get it to relax and slide out of its burrow without doing any harm to the worm. linear temperature gradient that went from 10°C to 25°C across the bottom of the experimental part of the apparatus. Within each one of quadrants the variability was low, with an average deviation of 3°C (Figure 5).
Results The chillers and heaters maintained steady temperatures in the cold and hot reservoirs throughout the experiment, with the cold reservoir at 5°C and the hot reservoir at 35°C. There was a temperature difference of 20°C between the two reservoirs (Figure 4). This set up a nearly
Figure 4: This graph compares the temperatures in the hot and cold reservoirs throughout the experiment. The reservoir temperatures held steady throughout the experiment.
Introduction to Scientific Research 2015–2016, Old Town High School
Figure 5: This box plot displays all the temperatures that were collected throughout the experiment in each quadrant. There are five groups of three. Each group of three shows the temperature measurements within each zone of the temperature gradient. The temperature gradient is nearly linear, with an average deviation of about 3°C within each zone. The results were collected by taking images of the P. websteri movements and measuring the distances the worms moved horizontally (x) and vertically (y). When a P. websteri was placed in the sediment that ranged from 15°C to 25°C it would move throughout the sediment to get to the 25°C part of the temperature gradient (Figure 6). Every P. websteri introduced within the above temperature range moved to the 25°C section of the temperature gradient. However, when a worm was introduced into sediment that was below 15°C it did not move. If the worm did move it was a very small movement that resembled an oval (Figure 7). All the movements were compared on one grid. The grid also compared the movements of the P. websteri in relation to the temperature gradient. This made it very clear that all of the worms moved to the 25°C temperature except for the two entered into the below 15°C sediment to begin with, both of which moved in the small oval-like pattern (Figure 8).
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a associate professor at the University of Maine School of Marine Sciences, has been looking for P. websteri in sediment samples. Our information about how well P. websteri can live in the sediment could give Dr. Lindsay’s project confidence for continuing. The finding that P. websteri can survive in the sediment for at least part of their lives could open up new “doors” for research. Scientists and growers may learn new behaviors of P. websteri such as their burrowing habits in sediment. Scientists could discover that P.
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Discussion/Conclusion Throughout this entire experiment the P. websteri lived and survived outside a mollusk host. Not only could the P. websteri live in the sediment, the data showed that they could also move “long distances” throughout the sediment. These data also support the possibility that P. websteri can live happily and survive the whole adult section of their life in the sediment. Knowing that the adults can live in the sediment for extended periods of time could allow scientists and oyster growers to learn more about the P. websteri life cycle and reproduction. Sara Lindsay,
C Figure 6: (A) The movement of one worm after one day. (B) The movement of two worms that were placed in two different quadrants. (C) The movement of two worms over three days. Numbers next to the track represent the number of days it took the worm to move that distance. The x= value is how far the worm moved horizontally and the y= is the distance the worm moved vertically. The red line indicates the worm moved toward the hot side of the temperature gradient and traces the track it left in the sediment.
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Introduction to Scientific Research 2015–2016, Old Town High School
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B Figure 7: (A) The movement of a worm that was placed near the cold reservoir side of the tank. (B) The movement of a second worm that was placed in the cold side of the temperature gradient. The blue arrows trace the worms’ tracks in the sediment and indicate that it was on the cold side of the temperature gradient. The number “1” indicates that the worm made this movement in one day. The x and y show the total distances the worm moved vertically and horizontally. The movements of the worms in (A) and (B) are almost identical.
websteri leave their tubes in the sediment at a certain time in their lives. Samples of sediment could be taken and if there are P. websteri in the sediment, scientists could genetic differences to test the idea that all P. websteri may not actually be the same species but that one group could be sediment-dwelling P. websteri and another group could be shell-dwelling P. websteri. Also,if larvae were released from sediment-dwelling P. websteri could they go and settle in an oyster, or must they settle back on the sediment? If they can go burrow in an oyster and breed with another P. websteri this would be a positive example of interbreeding within the species regardless of whether the adults live in the sediment or in a shell. These findings could help oyster farmers predict where adult sediment-dwelling worms would most likely be located in the estuaries they are using to farm their oysters. For example, if the oyster farmers took sediment temperatures at various spots in the estuary, they could test an idea that there are more P. websteri adults located in the warmer sediments of the estuary than in the cooler sediments. The temperature gradient in the experimental tank was very similar to the seasonal temperature change in the Bagaduce estuary (Figures 9 and 10). In the Bagaduce, P. websteri can’t move away from the seasonal temperature change but this similarity between the seasonal temperature gradient and my experimental temperature gradient
Figure 8: Comparison of all the worms’ movements to each other and to the temperature gradient. Each color arrow represents a different worm. The dotted arrow indicates a backwards movement and the solid arrows represent the initial movements. The temperatures at the top of the grid represent the median temperature for each zone.
Introduction to Scientific Research 2015–2016, Old Town High School
Figure 9: The water temperatures taken at a site in the oyster growing area of the Bagaduce river in the summer.
Figure 10: The water temperatures taken at the same site as Figure 12, but during the fall.
could help oyster farmers in the Bagaduce learn when P. websteri are likely to be the most active in the sediment. One thing that could be done to help improve these data is creating a larger tank to put the worms in so you could see if they can move even farther than they did in the smaller tank of this experiment. This information could be useful because knowing that the worms can move so freely throughout the sediment could help increase confidence that they can live their entire lives in the sediment, without a mollusk host. Finally, we think Jesse Leach would agree that pursuing research to reveal any new information about the life cycle and habits of P. websteri could lead to oyster farming practices that decrease the number of P. websteri-infested oysters.
Bibliography
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Mountford, M. D. “On E. C. Pielou’s Index of Non-randomness”. Journal of Ecology 49.2 (1961): 271–275. Web… Day, Randy and Blake, James. “Reproduction and Larval Development of Polydora Giardi Mesnil” (February 1979): 21 Print. Ingólfsson, Agnar. “The distribution of intertidal macrofauna on the coasts of Iceland in relation to temperature.” Sarsia 81.1 (1996): 29-44. Rawson, Paul. Personal interview. 4 March 2016
